Collaboration Agreement - Schedule of Potential Milestone Payments in Sales (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Milestone payments earned	$ 70.0	$ 50.0	$ 25.0

Sales milestone payments earned under collaboration agreement.

No definition available.

Name:	mdvn_SalesMilestonePaymentsUnderCollaborationAgreement
Namespace Prefix:	mdvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration